It may seem as though Twitter got things started on Sept. 12, when the company tweeted it had “confidentially submitted an S-1 to the SEC for a planned IPO.” But Twitter had actually made that submission about two months earlier, in July. The September announcement wasn’t required by law, but a source says Twitter intended to get out ahead of any press leaks and avoid a frenzy later on by simply making a public filing with no warning.

The S-1 will also reveal how much Twitter intends to raise in the IPO and how much each share will cost. Typically those figures are placeholders to be revised later after gauging market reaction, but in this case, they are likely to be closer to reality. That’s in part because Twitter has already been talking to potential large investors and getting a sense of their appetite, something that’s typically prohibited but which the JOBS Act allows.

Twitter’s IPO price is currently thought to be in the range of $28 to $30 a share, which would value the company between $15 billion and $16 billion. But those figures could still change quite a bit before the IPO.

That means the social media and microblogging company's stock could begin trading by late October or early November, if the offering moves at full speed.

Twitter announced earlier this month via a tweet that it had made a confidential filing with regulators. Under U.S. offering rules, the social media and microblogging company can propose a price and launch its offering as soon as 21 days after it makes a public filing.